Existing shock absorbers dampen automotive vehicle bounce and jounce by converting the energy stored in the compressed suspension springs into heat.
Present level control systems used in automotive vehicles consist of a pair of shock absorbers with integral air springs, a level sensing device mounted between the chassis and the rear axle, and a vacuum driven air compressor and reservoir mounted under the hood. This system has the advantage of immediately leveling the vehicle as soon as the engine is started, however, it is an expensive, complex and failure prone system.
The present invention is intended to provide a variable force as necessary to support a variable vehicle load at the predetermined level attitude. The variable spring force will be created by varying the pressure of the shock absorber fluid volume, the pressure will act upon the piston rod effective area to provide the spring force. The shock absorber fluid volume may include a compressible air volume or be filled with a compressible fluid. The system includes a coaxial piston pump within a piston rod which utilizes the axial motion of the shock absorber to pump fluid into or out of the shock absorber volume to vary the spring load. The system further includes position sensing which is accomplished by a bleed orifice through the hydraulic pump wall. As vehicle position changes the bleed hole is positioned to bleed and deactivate either the pump "up" or pump "down" portion of the hydraulic pump.
If the vehicle is loaded and must be raised to the level position the bleed orifice is positioned in the pump "down" cylinder rendering it ineffective. The pump "up" cylinder has no bleed so with each bounce and jounce fluid is pumped into the shock absorber volume until the vehicle is level. If the vehicle is unloaded and must be lowered to the level position the bleed orifice is positioned in the pump "up" cylinder rendering it ineffective. The pump "down" cylinder has no bleed so with each bounce and jounce fluid is pumped out of the shock absorber volume until the vehicle is level. Equilibrium is achieved when the bleed hole is centrally located and the fluid pumped into the shock absorber equals the fluid pumped out.